The present invention relates to a trimming device for trimming a top cover thread on a multiple needle sewing machine.
A trimming device is known, for example, from German Offenlegungsschrift No. 35 31 595, which describes a movable trimming knife for trimming a top cover thread, which is provided with a hook edge and which is moved mechanically backwards and forwards between a spreader and the workpiece from a diagonal upper rear direction towards the middle of the top cover thread. Because of the alignment of the trimmed top cover thread, this device requires the first new stitch between the top cover thread guide and a thread trap to be absolutely securely formed, because only in this way is it ensured that the cover thread is bound by the needle threads. In order to eliminate the risk of a missed stitch at the beginning of a seam, the starting needle threads required for stitch formation are annoyingly long. Following termination of sewing, these thread ends must be additionally shortened in order to obtain an optically acceptable sewn product.
A further trimming device for trimming the top cover thread is known from German Patent Specification No. 25 35 316. In this device, a thread pulling hook passes between a leaf spring and a presser foot and catches the top cover thread in order to trap it by means of the raised presser foot and the leaf spring. Then the top cover thread is trimmed by a thread trimmer between the leaf spring and the retracted thread pulling hook. This construction has a large number of parts and is thus expensive. Furthermore, the cover thread trimming operation cannot take place until the presser foot has been raised. This leads to a further time delay in production.
The trimming of the remaining sewing threads at the end of the seam is generally known and is described, for example, in German Patent Specification No. 25 38 916.